It is well known that a homogeneous transition metal catalyst has a very high catalytic activity in an olefin polymerization, such as a non-supported Zeigler-Natta catalyst, a metallocene olefin polymerization catalyst, a geometrical configuration-constrained olefin polymerization catalyst, or a nonmetallocene olefin polymerization catalyst. The nonmetallocene olefin polymerization catalyst has a coordination atom including oxygen, nitrogen, sulfur and carbon and the like, contains no a cyclopentadiene group, and was developed in the earlier 1990s. The catalyst has a catalytic activity near to or even higher than that of a metallocene olefin polymerization catalyst, but retains the advantages of a metallocene catalytic system, such as controllable polymer forms, narrow molecular weight distribution, capable of scission to the polymer molecule, and adjustable polymer molecular weight and branching degree, and the like. Furthermore, since this kind of catalyst has a weak oxyphilicity, the copolymerization of a polar monomer with olefins can be realized, thereby a functionalized polyolefin materials with excellent properties can be produced.
In case of a homogenous polymerization, the formed polymers would stick on the reactor tank or adhere to the stirring puddle, which has serious influences on the normal operation of the reactor and the heat exchange of the reaction mass inside the reactor, thus hindering the continuous production in industry. In addition, in the homogeneous catalyst system, a large amount of a co-catalyst, for example, methylaluminoxane, is required, thus increasing the production cost of polyolefins, and adversely influencing the properties of the products due to the large amount of co-catalyst introduced, in some cases, the aluminum component introduced during the polymerization process may have to be removed in a post-processing step, thus further increasing the process cost. A catalyst or catalytic system for olefin polymerization and copolymerization prepared in WO 03/010207 is applicable to a wide range of olefin polymerization and copolymerization, useful for various kinds of polymerization processes. However, in case of an olefin polymerization, a larger amount of co-catalysts is required in order to obtain an appropriate activity in the olefin polymerization. Furthermore, the phenomena of stick on the tank often occurs during the polymerization process.
Based on the experience of the metallocene olefin polymerization catalyst in the industry (Chem Rev, 2000, 100: 1347; Chem Rev, 2000, 100: 1377), support of a homogeneous nonmetallocene olefin polymerization catalyst is rather necessary.
The main object of supporting a catalyst is to improve the polymerization performances of the catalyst and the granule morphology of the resulted polymers. Support of a catalyst results in some how decrease of the initial activity of the catalyst, thus decreasing or even avoiding the occurrence of agglomeration or flash polymerization during the polymerization. After supported, the polymer morphology can be improved and the apparent density of the polymer can be increased. A supported catalyst is applicable to more types of polymerization than a unsupported one, such as a gas-phase polymerization or a slurry polymerization and the like, furthermore, the supporting process can greatly decrease the cost for preparing the catalyst and for polymerizing olefins, improve the polymerization behaves, and elongating the serve life of the catalyst used, and so on. In EP 0206794, by using a MAO modified oxide carrier and a metallocene, the influence of the properties of the carrier material on the graininess of the resulted polymer products is restricted. In EP 685494, the bulk density of the polymerization product may be decreased by reacting methylaluminoxane with a hydrophilic oxide, using a polyfunctional organic cross-linking agent and then an activated MAO/metallocene complex, as a result, it is not appropriate for an industry use.
In patent CN 1352654, an organoaluminum, an organosilicon, an organomagnesium and an organoboron compound are used for treating a carrier, and then supported thereon a single-site olefin polymerization catalyst containing a heteroatom ligand, thus a supported catalyst is obtained with high activity and long storage period. EP 295312 describes that an aluminoxane solution contacts with a solvent unable to dissolve the aluminoxane in the presence of an organic or inorganic granulate carrier to make the aluminoxane precipitate on the carrier. WO 97/26285 describes a method for preparing a supported metallocene catalyst under high pressure, resulting in a prolonged production cycle and lowered supporting efficiency. Further, in CN 1307065, a metallocene catalyst is supported on a carrier which has been treated with an alkylaluminoxane under ultrasonic oscillation. But the supporting process is not economic.
In order to increase the bonding strength between the carrier and the catalyst, CN 1162601 uses a bifunctional cross-linking agent to treat a carrier which has been treated with an aluminoxane or an alkylaluminum compound previously. In patent CN 1174849, a metallocene catalyst is supported on a dehydroxylated silica having been treated with MAO in a toluene media, but no polymerization activity data of the supported catalyst are given in the specification. Patent CN1120550 proposes a method for supporting a catalyst, mainly comprises that, a hydrophilic, macroporous and finely divided inorganic carrier is heat-activated, then reacts with an aluminoxane, further reacts with a multi-functional organic cross-linking agent, finally mixed with the reaction product of a metallocene and an activator, thus a supported metallocene catalyst is prepared. But the aluminoxane is used in a high amount in the supporting process. In CN 1053673, by contacting with each other a catalyst and a co-catalyst supported on a carrier material in a suspension under a microwave, a supported catalyst with a stable structure is prepared. However, this method needs a microwave generating apparatus and the operation is rather complicated. In CN1323319, a porous particle carrier in a flowable form is impregnated with a catalyst material, that is to say, a solution of the catalyst is sprayed onto the carrier in a amount by volume corresponding to the pore volume of the carrier, then dried to obtain a supported catalyst. The supporting method requires that the catalyst is sufficiently soluble in the solution, otherwise the supported catalyst can not be guaranteed with respect to the supporting uniformity and the loadinging of the catalyst. Patent WO96/00243 describes a method for preparing a supported catalyst composition. The method comprises mixing a bridged bis-indenyl metallocene with an aluminoxane in a solvent to form a solution, and then combining said solution with a porous carrier, wherein the total volume of the solution is less than that necessary for forming a slurry.
The catalyst prepared using anhydrous magnesium chloride as a carrier exhibits a higher catalytic activity in the olefin polymerization, but this kind of catalyst is very brittle, prone to crush in the polymerization reactor, resulting in a poor polymer morphology. The catalyst supported on silica has an excellent flowability, useful to a fluidized-bed gas-phase polymerization, but the silica-supported metallocene and nonmetallocene catalyst shows a lowered catalytic activity. If magnesium chloride could be appropriately combined with silica, a catalyst with high catalytic activity, controllable granule size and good abrasion resistance may be obtained.
EP 0878484 reports that the catalyst prepared by supporting a zirconocene on a dual carrier of MgCl2/SiO2 having a low magnesium chloride content (less than 3%) can be used for homopolymerization or copolymerization of ethylene, with an improved catalytic activity.
Patent CN 1364817 discloses a method for preparing β-diketone semi-titanocene catalyst supported on a magnesium chloride/silica carrier, and use of the supported catalyst in olefin polymerization, with a polymerization activity of 7.42×106 g polyethylene/mol titanium·hr in the polymerization of ethylene. But the patent gives no specific data on the granule properties of the polymers.
Patent EP260130 proposes that a metallocene or nonmetallocene catalyst is supported on a silica carrier having been treated with methylaluminoxane, the nonmetallocene mentioned therein is only confined to ZrCl4, TiCl4 or VOCl3. The patent deems that the most preferred is that the carrier surface is treated with an organo-magnesium compound or a mixture of a magnesium compound and an alkylaluminum. However the proposed process is relatively complicated and requires many preparation steps.
Patent CN1539856A proposes that a nonmetallocene catalyst is supported on a composite carrier formed of silica and magnesium chloride, and further a catalyst system for polymerization is formed from the supported nonmetallocene catalyst obtained from this method and methylaluminoxane. The catalyst system is used for an olefin polymerization.
Patent WO 03/047752A1 and WO 03/047751A1 provide a method for supporting a composite catalyst (a Zeigler-Natta catalyst and a metallocene catalyst, or a nonmetallocene catalyst and a metallocene catalyst) on silica. The patent uses a chloride or oxychloride of titanium or vanadium as a nonmetallocene catalyst component. Therefore, the obtained catalyst is a bimetallic catalyst.
The activity of an olefin polymerization catalyst in an olefin polymerization is a primary requirement for the catalyst. However, after the nonmetallocene catalyst is supported on an inert carrier, its catalytic activity in the olefin polymerization is more or less decreased, in some cases, the activity is even decreased by one order or more, resulting in a uneconomic use of the supported catalyst. What is more is that, after the activity is decreased, ash is increased in the obtained polymer, and a step for deashing needs to be added in the production, resulting further in the increment of the cost and the complexity of the production plants, thus restricting its further use in production of polyolefins.
With regard to the polymerization technology, there are several polymerization systems in industry, each of which is based on a different catalyst, including: a high pressure process, in which the polymerization pressure is higher than 50 MPa, using an stirred tank or a tubular reactor. It was firstly developed by Exxon. Exxon is now producing a product Exact® in a high pressure polymerization plant at Baton Rouge using an Exxpol® single-site catalyst. The product has a property between an elastomer and a low density polyethylene. But the high-pressure process has very severe requirements for equipment and costs quit a large of capital investment. A solution process is relatively suitably used with a homogeneous single-site catalyst. In 1993, Dow used a CGC catalyst to produce plastomers and elastomers using an Insiteg technique at Taxas, subsequently using the Insite® technique at Tarragona, Spain, to produce elastomers, plastomers and enhanced LLDPE, i.e. Engage®. In 1996, a plastomer Affinity® and an elastomer Engage® were produced in a plant at LA. Hoechst, Nova, Dex Plastomers and MITSUI Oil Chemical have developed its solution process. More interest has been given to a gas-phase process recently. It is simple in process, cheap in cost, wide in product specification, and is especially suitable for copolymerization. BASF, UCC, BP MITSUI, Montell, and Borealis have developed its gas-phase process, in which, the fluidized bed developed by UCC and BP, and the stirred-bed reactor developed by Elenac are most typical. A slurry process has achieved a wide use in industry. Phillips' and Solvay's loop process reactor, Elenac's stirred-tank reactor, Nissan's and MITSUI's double tank stirred reactor are most typical in industry. The slurry process encounters no a stirring problem associated with the viscosity, the reaction is conducted in a homogeneous medium, the reaction heat is easy to be removed and the polymerization yield is high, therefore, it can produce polymers of very high weight-average molecular weight. It needs less energy to recover the resulted polymers, with a low investment and production cost.
WO 9729138 discloses that in a fluidized-bed reactor, homopolymerization of ethylene can be enhanced by decreasing the ethylene partial pressure and using different polymerization temperatures, the best result is obtained by using an ethylene partial pressure of 60 to 120 Psi and a reaction temperature of 90 to 120° C. The patent discovers that the homopolymerization of ethylene is independent of the types of the metallocene supported.
When a polymerization technology is to be chosen for a catalyst, what need to be taken into consideration is the compatibility between the polymerization technology and the catalyst, the investment cost, and the complexity and cost for running this apparatus, and to what extent the polymerization product properties can be controlled by the polymerization technology, and the influences of a variation of the polymerization conditions on the properties of the products. The high-pressure process and the solution process are both relatively suitable for a non-supported metallocene or nonmetallocene catalyst, while the gas-phase process and the slurry process are more suitable for a supported metallocene or nonmetallocene catalyst.
For industrial use of a novel supported nonmetallocene catalyst, the key point lies in the adaptability of the catalyst to a existing system. A most preferred situation is that, only by adjusting slightly the existing system, the use of this supported metallocene catalyst in an existing industrial apparatus can be realized. Patent U.S. Pat. No. 5,352,749 describes a modification on the existing system in case of mPE, which comprises, a modification on monomer purifying step, catalyst storage, formulation, treatment and feeding; a strengthened hydrogen regulation system; and improvement on the extrusion system.